The present invention relates to an optical switch, in particular, relates to such a switch which is small in size and switches at high speed.
FIG. 1 is one of the prior optical switches, in which the reference numeral 1 is an input optical waveguide, 2 is an output optical waveguide, 3 is a lens for providing parallel optical beam, 4 is a movable mirror. The optical switch of FIG. 1 switches an optical signal by inserting or removing mechanically a mirror in or from an optical path. Since the mechanical movement of a mirror is essential in FIG. 1, the operational speed of the switch of FIG. 1 is rather slow as a few milliseconds, and the size of a switch can not be small.
FIG. 2 is another prior optical switch of a directional coupler type, in which the reference numeral 5 is an electrode, 6 is an electro-optic crystal, for instance, LiNbO.sub.3 or LiTaO.sub.3 for controlling the coupling degree of a directional coupler. The optical switch of FIG. 2 has the disadvantages that (1) cross talk level is high, for instance the cross talk level reaches even -10 dB or -20 dB, (2) the allowable manufacturing error is very severe, (3) a DC bias voltage is necessary, (4) an insertion loss is large, and (5) a long substrate is necessary when a large scale equipment is constructed.
Another prior optical switch uses a liquid crystal or electro-optical reflector as shown in West Germany Auslegeschrift No. 2238336, and U.S. Pat. No. 4,065,729. The former performs an optical switching through the control of polarization, but has the disadvantage that the switching speed is very slow, and it takes about 50 msec for each switching. The latter performs the optical switching through the control of the refractive index, but has the disadvantages that cross talk level is high, the insertion loss is high, and the voltage for performing the switching must be high.
Another prior optical switch is shown in the article "Electroabsorption in Al.sub.y Ga.sub.(1-y) As-Al.sub.x Ga.sub.(1-t) As double heterostructures" by F. K. Reinhart, in Appl. Phys. Letters, vol. 22, pp. 372-374, 1973. This switch uses the Franz-Kerdish effect, and has the nature of high speed switching. However, it has the disadvantages that the isolation is poor, and the insertion loss is large.
Another prior optical switch is shown in the article "Design and development of a high-speed electro-optic A/D converter" by F. J. Leonberger, et al, in IEEE Trans. CAS-26, pp. 1125-1131, 1979. This switch has the nature that the switching speed is high, but the isolation is poor, it needs DC bias voltage, the insertion loss is high and it has the polarization dependence of switching.
Another prior optical switch is an optoelectronic switch, which has a photo-diode. The switching of the bias voltage of the photo-diode performs the switching from an optical signal to an electrical signal. This switch has the nature of the wideband, the high isolation, and the high speed switching operation, but has the disadvantage that an output electrical signal must be converted to an optical signal further for providing an optical switch.